Patent GB-190622863-A (GB)
Title: Improvements in or relating to the Speed Regulation of Induction Motors.
Inventor: MILCH MAURICE
Filed: 1906-10-16
Granted: 1907-07-18
Abstract: 22,863. Milch, M. Oct. 16. Motors, controlling.-In order to regulate within narrow limits the speed of induction motors, an auxiliary electromotive force of the same number of periods as the electromotive force induced in the armature is produced outside the armature, and is introduced always at the same point of the induced armature winding. The apparatus employed to give an electromotive force introduced into the armature corresponding, as regards the number of periods, to the electromotive force induced in the armature consists of an armature winding provided with a commutator, and supplied with current from the same source as the motor to be regulated. The armature or the brushes of the auxiliary apparatus are rotated synchronously with the rotor of the motor. If the voltage of the circuit is high, it may be transformed down before applying it to the regulating-apparatus, either by means of a separate transformer or by a secondary winding on the regulating-machine. The currents obtained are fed directly into the secondary member of the motor, or are used to excite the field of a commutator dynamo suitably driven, which will generate electromotive forces of the frequency of the exciting-currents employed to feed the secondary of the motor. Fig. 1 shows a three-phase motor 13,14 regulated by means of current derived from an auxiliary winding 4 through brushes 10 and regulating-resistances 11. The current for the regulator 4 is obtained from the mains through a transformer 9. In starting, the auxiliary apparatus is switched out and starting-resistances 17 are employed. When two motors are employed, of which the second is used in cascade only, the second motor may be provided with a commutator as well as slip rings, so that it may supply the electromotive forces for regulating the speed of the first motor when the latter is working alone. To regulate the speed of two motors which may be connected in cascade or multiple, a separate winding is employed which is connected to the secondary member of the leading motor respectively to the multiple - connected secondary members of both motors when working in multiple, and to the secondary of the "led" motor when in cascade. To counteract the alteration of the power factor produced when altering resistances or changing speed, the relative phase of the auxiliary electromotive force may be varied by shifting the brushes 10, the winding 4, or the points of connexion of the leads 6 to the winding 4, and apparatus for effecting this may be combined with that for varying the resistances 11. The employment of a commutator dynamo 22, 23, 24, excited by currents from a winding 4 having brushes 10 rotated synchronously with a motor 13, 14, is illustrated in Fig. 3 in connexion with a two-phase system. The dynamo is driven by any motor at any speed, and is provided with compensating - windings 23 to counteract the electromotive forces in each phase of the commutator winding 24 induced by the dynamo field excited by the winding 22. Regulating and starting resistances 11, 17 are provided, as in the previous arrangement.